Capsular polysaccharides (cps) are important immunogens involved in various bacterial diseases. This feature has lead to them being an important component in the design of vaccines. They have proved useful in eliciting immune responses especially when linked to earner proteins [1]. Typically, capsular polysaccharides are produced using batch culture in complex medium (Group B Streptococcus, Staphylococcus aureus, Streptococcus pneumoniae and Haemophilus influenzae), fed-batch culture (H. influenzae) or continuous culture (Group B Streptococcus and Lactobacillus rhamnosus) [2-7]. Most studies used batch culture systems in which the growth rate, nutrient levels and metabolic concentrations change during incubation. In such systems, alteration of one factor results in changes in other factors associated with growth. Continuous cultures allow the researcher to separate and define parameters that are interdependent during batch culture growth, such as growth rate, nutrient and product concentrations and cell density. During continuous culture, fresh medium is added to a culture at a fixed rate and cells and medium are removed at a rate that maintains a constant culture volume. Continuous culture was preferred for capsular polysaccharide production when it proved to be dependent on conditions [8].
For Group B Streptococcus (GBS, S. agalactiae), cell growth rate was reported to be the principal factor regulating capsular polysaccharide production. Furthermore, the production of type III capsular polysaccharide was shown to occur independently of the growth-limiting nutrient. Higher specific yields (up to about 90 mg/gDW) were obtained when cells were held at a fast (0.8, 1.4 or 1.6 h) mass doubling time [td] rather than at a slow time (td=2.6 or 11 h) [8-10]. However, continuous culture is prone to strain stability problems and contamination. Furthermore, continuous culture is somewhat expensive due to the continuous feed of medium and nutrients.
There is therefore a need to find alternatives to continuous culture for the high yield production of capsular polysaccharides in order to overcome the problems with continuous culture that are cited above.